The present invention relates to a communication network system, a gateway, a data communication method, and a program providing medium, more specifically, to a communication network system, a gateway, a data communication method, and a program providing medium, which enable data communication having advanced functionality by adding functions of routing information providing processing and authentication processing to a gateway that performs communication protocol conversion between a public communication network and a private communication network such as LAN.
A gateway is used as a device that enables interconnection between a public communication network such as Internet and telephone line and a private communication network such as LAN. The gateway provides mutual communication by performing communication protocol conversion between the public communication network and the private communication network. The gateway is also used in mutual protocol conversion between LANs (Local Area Network) that are constructed as private communication networks. A typical example of LANs is Ether-net, which provides connections of two or more communication terminals including personal computers on a single cable. As a method for avoiding a collision of packets transmitted and received on two or more computers, and the like, CSMA/CD (Carrier Sense Multiple Access/Collision Detection) is adopted.
As conventionally known connection devices for communication networks, for example, there are a modem unit that performs digital-to-analog conversion to connect an analogue telephone to a digital line, a hub that performs connection processing at the physical layer level of OSI layers, a repeater, a bridge that performs processing at the data link layer level of OSI layers, a router that performs processing of the network layer of OSI layers, and the like. Main functions of the repeater are amplification processing and distortion restoring processing to restore a signal level attenuated in the process of transmission. The bridge has a function of performing filtering processing for checking a source (originator) address and a destination (recipient) address, which are managed by the data link layer, to determine whether or not a packet is to be transmitted. The router has a function of relaying and exchanging packets according to protocol definition of the network layer. The gateway has an overall exchange function that is adaptable to OSI layers from the first to the seventh layer, that is to say, from the physical layer to the application layer. The gateway, therefore, provides connection between different networks.
However, because the various kinds of communication network connection devices described above are devised to provide only mutual communication with a network having a different protocol, there is no communication network connection device that has an application involved in processing with advanced functionality including functions of routing information providing processing and authentication processing for various kinds of terminals such as personal computers connected to a network.